The Periodic Table Cl 35.5 Br 79.9 I 126.9 History of the Periodic Table J.W. Dobereiner – elemental triads Elements in a triad have similar properties The properties of the middle element are ~ averages of the others Element Atomic Mass Cl 35.5 Br 79.9 I 126.9

The Periodic Table J.A.R. Newlands – Law of Octaves Arranging elements by increasing atomic mass results in every 8th element having similar properties Demonstrated that there is a pattern to elemental properties

The Periodic Table Dmitri Mendeleev Arranged elements in order of increasing atomic mass and made a table Switched the order of some elemental pairs to make them fit

Mendeleev’s Periodic Table

Comparison of Ekasilicon and Germanium The Periodic Table Mendeleev predicted the properties of undiscovered elements: Comparison of Ekasilicon and Germanium Property Ekasilicon Germanium Atomic Mass (amu) 72 72.59 Density (g/mL) 5.5 5.35 Melting Pt. (oC) High 947 Color Gray

The Periodic Table Henry Moseley – discovered that the correct way to arrange the elements is in increasing order of atomic number

Periodic Law When elements are arranged in order of increasing atomic number, their physical and chemical properties show a periodic pattern

Group - vertical columns (1-18)

Period – horizontal row (1-7)

Family Names Groups 1-2; 13-18 – Representative Elements Group 1 - Alkali Metals Group 2 – Alkaline Earth Metals Group 3 to 12 – Transition Metals Group 13 – Boron Family

Family Names Group 14 – Carbon Family Group 15 – Nitrogen Family Group 16 – Chalcogens Group 17 – Halogens Group 18 – Noble (Inert) Gases

Periodic Table The lanthanoid and actinoid series are known as the InnerTransition Metals Hydrogen – not really a member of any group – definitely a nonmetal in physical properties but has certain chemical properties similar to the group 1 elements

Metals, Nonmetals, and Semimetals Shiny luster Conduct electricity Conduct heat Usually solid at room temperature Malleable Ductile Gold Nugget

Metals, Nonmetals, and Semimetals Dull luster Poor electrical conductor Poor conductor of heat Many are gases at room temperature Brittle Sulfur

Metals, Nonmetals, and Semimetals Semimetals (metalloids) Properties of both metals and nonmetals Semiconductors B, Si, Ge, As, Sb, Te, At Silicon

Periodic Trends Periodic Trends – predictable changes in the properties of the elements as you move through the periodic table

Periodic Trends Atomic Radius – the distance from the center of an atom to its outermost electron Atoms become larger as you go down a given group Atoms become smaller as you go from left to right in a given period

Periodic Trends Ionic size Ions increase in size as you go down a given group Metal and nonmetal ions decrease in size as you go from left to right in a given period